RELATIVISTIC CONFIGURATION-INTERACTION CALCULATION OF THE POLARIZABILITIES OF HELIUM-LIKE IONS

Polarizabilities of ions of the helium isoelectronic sequence with nuc lear charges in the range 2 less than or equal to Z less than or equal to 30 are evaluated starting from the relativistic no-pair Hamiltonia n and including both the Coulomb and Breit interactions. The ground st ate and perturbed wave functions are expanded in two-electron basis fu nctions constructed from B splines. For each ion, the ground-state wav e function is determined by a configuration interaction calculation; t he perturbed wave function is then found by solving an inhomogeneous a lgebraic equation. Nonrelativistic calculations are carried out in par allel with the relativistic calculations, permitting relativistic corr ections to be isolated. The present nonrelativistic calculations are f ound to be in good agreement with other precise calculations. For the experimentally interesting case of heliumlike lithium, we obtain the v alue Delta alpha(Rel) = - (4.50 +/- 0.05) x 10(-5) a.u. for the relati vistic correction to the ground-state polarizability.